One aspect of the pattern recognition problem is identifying an object as a member of a class of objects. We propose a simple optical method of performing this task by taking advantage of the response of a classical matched filter (CMF) used in an optical correlator. The CMF has been shown to have a broad correlation peak while the response of a phase-only filter (POF) is quite sharp. Previous studies have shown that the POF is very sensitive to an exact pattern match where a CMF is less sensitive. This feature of the CMF implies, in some cases, it could be used to advantage in detecting a class rather than a specific object. Unfortunately, the CMF, which is a complex valued filter containing both amplitude and phase, has been implemented only on photographic film using holography. This is impractical in a real-time system. Further, as the correlation information is located in the higher diffraction orders, holographic schemes have low light efficiences. A CMF filter contains a complex function Since a complex number is represented as a point on the complex plane, it is necessary to describe it by a real and imaginary part (both of which are real numbers) or by a magnitude and a phase angle (real numbers). Regardless, two pieces of information are needed to specify a complex number. Filter media whether photographic film, an etched quartz substrate, or a spatial light modulator (SLM) can only store one real function. VanderLugt used holographic techniques to solve this dilemma by encoding the CMF data on a spatial carrier frequency. In recent years, it has been demonstrated that optical correlation is much more sensitive to the phase information from the reference image transform. Amplitude is set to one over the entire filter. The POF is represented mathematically by a real function and could be written directly on a media. Because it is not necessary to use holography, the effective diffraction efficiency (Horner efficiency) for the POF is nearly 100%, and the correlation information is found in the zeroth order. See U.S. Pat. Nos.4,588,260, 4,765,714 and 4,826,285, to J. Horner, incorporated by reference herein For further background information see also our articles published in "Applied Optics" 1 May 1989, Vol. 28, No. 9; and in "Optical Engineering", May 1989, Vol. 28, No. 5.